"Since the iPod was introduced in Oct. 2001 it has been the primary driver of the company's growth engine," analyst Gene Munster wrote in a note to clients. "We are modeling for the year-over-year growth to stabilize at [approximately] 20 percent, but believe 30 percent growth is achievable and will provide upside to our estimates."

While noting that Apple has sold 68 million iPods in the past five years (of which 39 million were sold in the last year), the analyst maintained his belief that a "significant addressable market" remains.

"Although we consider it an overestimation, if we use the mobile phone market as a proxy for the Pod's addressable market, then the iPod's market penetration is [currently] about 27.5 percent," he said.

Over the next 6 months, Munster expects Apple's forthcoming iPhone and iTV set-top media device to account for two more significant drivers to the company's growth engine.

"The mobile phone market represents a large potential supplement to iPod sales," he told clients. "Music-enabled phones are gaining popularity, but Apple will be the first to offer a unified solution with the design and usability of the iPod."